1. Field of the Invention
This invention deals with transferring solid materials from one conveyor to another travelling in a different direction.
2. Description of the Prior Art
Conveyor belts are widely used to move large tonnages of material. When a sudden change in horizontal direction is required it is usually necessary for the material to be transferred to another belt travelling in the new direction.
Conveyor belts used for transferring large quantities of bulk material vary in width between 12 inches and 108 inches with 36 inches to 84 inches being common. They usually travel at 150 feet per minute to 1200 feet per minute with 200 feet per minute to 800 feet per minute being a common range. Such belts generally handle between 200 tons per hour to 20,000 tons per hour with 1,000 to 10,000 being common.
It is normal to have the end of the first belt raised several feet above the receiving belt and to employ a vertical box-like structure, at this location, (usually referred to as the "transfer point") to guide the material from the first to the second belt. The prior art has, in some cases, utilized fixed deflector plates, within this structure, to assist in changing direction of the material and also to contain the flow within the physical dimensions of the receiving belt, to reduce spillage.
The flow on the first belt or feeder belt is not always even and there are sometimes large surges in flow which can cause a boiling effect with the structure at the transfer point. A large surge can cause the "transfer" to block with material and cause spillage and also damage the conveyor belt.
Several other problems also exist with these transfer points, as they now exist. Two separate changes in direction take place, each of approximately 90.degree.. First, when the material, in its trajectory from the end of the first belt, is guided vertically downwards, and second, when the material contacts the second belt and is accelerated in a different direction. This second change in direction causes accelerated belt wear and uses additional energy.
Fixed deflector plates, within the box-like transfer structure, are also subject to excessive wear from friction created between the moving material and the fixed material of the deflector plates. Foreign objects such as tramp iron or frozen lumps of material, are frequently unable to make the turns and lodge within the transfer structure and block the flow and/or damage the receiving belt. This may cause plugging of the transfer structure, which may require a shut-down of the system to permit removal or dislodgement of the surplus or foreign material. Degradation of the material being handled may also occur due to the impact between the lumps during the two 90.degree. turns. An example of this is the degradation of iron ore pellets by striking against each other causing particles to break off and sometimes even causing the pellets to break down into powder, reducing the value of the material delivered.
In an effort to eliminate some of these problems, abrasive resistant steels or alloys have been introduced into the structure of the transfer devices to better withstand the constant impact. Greater horsepower has also been provided on the drive of the receiving belts to cater to the re-acceleration of the bulk material. It has been found desirable in some cases to increase the horsepower of short receiving belt drives by as much at 50% to accommodate overloads caused by surges.
Specially designed impact rollers are often positioned below the section of belt below the transfer box to cushion the vertical fall of the material and thus increase belt life. Impact rollers are usually of steel construction, with rubber tires mounted on them over the entire length.